As a method of detecting an orientation toward which a vehicle travels, that is, a vehicle orientation (a heading orientation), there is a method of calculating the vehicle orientation with orientation information calculated from a global positioning system (GPS) signal, or a method of calculating the vehicle orientation with a gyro. In the method of calculating the vehicle orientation according to the GPS signal, when a vehicle speed is slower, a travel distance for each time becomes shorter, and a calculation precision in the vehicle orientation is deteriorated. Thus, a method of calculating the vehicle orientation with the orientation information calculated according to the GPS signal when the vehicle speed is equal to or greater than a reference speed, and calculating the vehicle orientation with the use of the gyro when the vehicle speed is less than the reference speed has been proposed.
However, when the method is used, the following drawbacks may arise. For example, when a limit travel is performed in, for example, a circuit, a situation such as a drift in which tires are not gripped on a road surface may occur. In this case, by the above method, even when the vehicle speed is equal to or greater than the reference speed, the vehicle orientation calculated on the basis of the GPS signal may be different from an actual vehicle orientation, and an accurate vehicle orientation may not be calculated.